Semiconductor memory device

ABSTRACT

A semiconductor memory device comprising a plurality of row decoders, each having a precharge circuit connected to receive a precharge signal and a decode circuit connected to receive address signals. A level-shifted precharge signal is input to the precharge circuits.

The present application is a continuation of prior application Ser. No.09/168,673, filed Oct. 9, 1998, which is a continuation of priorapplication Ser. No. 08/907,030, filed Aug. 6, 1997 (now U.S. Pat. No.5,838,629), which is a divisional of prior application Ser. No.08/696,738, filed Aug. 14, 1996 (now U.S. Pat. No. 5,793,695), which isa divisional of prior application Ser. No. 08/379,290, filed Jan. 27,1995 (now U.S. Pat. No. 5,825,714).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory device, and moreparticularly to a word-line selecting circuit for selecting and drivinga word line.

2. Description of the Related Art

As the integration density of the semiconductor memory increases, it isincreasingly demanded that the power-supply voltage VCC of the memory bereduced and that the data be read from the memory faster.

FIG. 1 shows conventional word-line selecting circuits which areidentical and incorporated in a semiconductor memory. As illustrated inFIG. 1, each word-line selecting circuit has a P-channel MOSfield-effect transistor (PMOSFET) and an N-channel MOS field-effecttransistor (NMOSFET). A boosted potential VPP is applied to the sourceof the PMOSFET. The potential VPP is higher than the power-supplyvoltage VCC applied to the circuit from an external power supply. Thepotential VPP is generated by, in most cases, a boosted potentialgenerating circuit (not shown) which is provided in the memory chip. Aground potential VSS is applied to the source of the NMOSFET.

The PMOSFET and the NMOSFET are connected at their drains. The node ofthe drains of the MOSFETs is connected to one end of a word line WL.Connected to the word line WL are memory cells, only one of which isshown in FIG. 1. The gates of the PMOSFET and the gate of the NMOSFETare connected to each other. The node of the gates is connected by alevel-shifting circuit to a row decoder. The power-supply voltage VCC isapplied to the row decoder. The row decoder is controlled by controlsignals such as address signals and precharge signals, to generate anoutput signal S_(VCC) which is a VCC-based signal. The level-shiftingcircuit changes the level of the output signal to generate a VPP-basedsignal S_(VPP) whose high level is equal to the VPP level. The signalS_(VPP) is supplied to the gate of the PMOSFET and to the gate of theNMOSFET.

In the word-line selecting circuit of in FIG. 1, the PMOSFET is providedbetween the word line WL and the boosted potential VPP terminal in orderto drive the word line WL. The PMOSFET is used in place of a boot-strapcircuit which is incorporated in the ordinary word-line selectingcircuit. The boot-strap circuit is comprised of an NMOSFET for driving aword line and an isolation transistor, in order to lower thepower-supply voltage and shorten the time for selecting a word line.

With the word-line selecting circuit of in FIG. 1, wherein the PMOSFETis used in place of a boot-strap circuit, it is required that thecontrol signal supplied to its gate be a VPP-based signal whose highlevel is equal to the VPP level. This is because the PMOSFET would notbe turned off completely by a VCC-based signal at its high level (i.e.,the VCC level) since the source voltage of the PMOSFET is set at theboosted potential VPP. Although the PMOSFET must be controlled by aVPP-based signal, the output signal of the row decoder is a VCC-basedone. It is therefore necessary to convert the VCC-based signal to aVPP-based signal. This is why the level-shifting circuit isindispensable to the word-line selecting circuit shown in FIG. 1.

A memory device of this type is disclosed in, for example, U.S. Pat. No.4,344,005.

U.S. Pat. No. 4,344,005 also discloses a word-line killer circuit aswell as a level-shifting circuit. The word-line killer circuit sets aword line at the ground potential when a boosted potential VPP isapplied to another word line. The word-line killer circuit is driven bya killer-driving circuit. Like the level-shifting circuit, thekiller-driving circuit uses the boosted potential VPP as power-supplyvoltage.

FIG. 2 shows another conventional word-line selecting circuit. Thiscircuit includes two PMOSFETs (shown in the broken-line box LS) whichcorrespond to the level-shifting circuit used in the circuit of FIG. 1.The PMOSFETs are incorporated in the row decoder section for one wordline and have their gates cross-connected.

A memory device of this type is disclosed in, for example, IEEE Journalof Solid-State Circuits, Vol. 26, No. 8, August 1991, pp. 1171-1175.

Jpn. Pat. Appln. KOKAI Publication No. 4-106794 discloses an EPROM. Inthe EPROM, address signals are level-shifted before they are input to arow decoder.

The use of the two types of the conventional word-line selectingcircuits, both described above, is disadvantageous in the followingrespects.

The memory devices shown in FIGS. 1 and 2 need to have a number oflevel-shifting circuits. This is because each word-line selectingcircuit must be provided with one level-shifting circuit. Moreprecisely, exactly as many level-shifting circuits as the word lines arerequired in the memory devices of FIGS. 1 and 2.

Similarly, a memory device wherein address signals are level-shiftedbefore they are input to a row decoder must have a number oflevel-shifting circuits. This is because one level-shifting circuitneeds to be provided for each address-signal line.

The greater the number of level-shifting circuits provided, the largerthe chip size. Further, the larger the number of level-shiftingcircuits, the greater the consumption of power used to generate theboosted potential VPP. This is because each level-shifting circuit usesthe boosted potential VPP as power-supply voltage.

The consumption of power used to generate the boosted potential VPPincreases also when circuits using the boosted potential VPP aspower-supply voltage are provided in chips in large numbers.

As the consumption of power used to generate the potential VPPincreases, the boosted potential VPP is more likely to vary. Inparticular, a low boosted potential VPP tends to vary lower. To suppressthe the variation of the potential VPP, a sufficiently high potentialmust be applied to the boosted potential line. In order to apply such apotential to the boosted potential line, the capacitor incorporated inthe boosted-potential generating circuit needs to have a large area. Thelarger the area of the capacitor, the larger the chip size.

Third, the level-shifting circuit may cause errors since it must belocated adjacent to the memory-cell region due to the chip-layout and isinevitably influenced by the noise generated in the memory-cell array.The higher the integration density of the memory, the greater theinfluence the noise imposes on the level-shifting circuit. The word-lineselecting circuit is very likely to cause errors if incorporated in a64-MB or 256-MB dynamic RAM.

SUMMARY OF THE INVENTION

In view of the foregoing, a first object of this invention is to providea semiconductor memory device which has a relatively smallperipheral-circuit region and consumes relatively little power.

A second object of the present invention is to provide a semiconductormemory device which not only has a relatively small peripheral-circuitregion and consumes relatively little power, but is also lesssusceptible to influence by noise and can operate reliably.

To attain the first object, according to a first aspect of the presentinvention a semiconductor memory device is provided having a pluralityof row decoders, each connected to receive a precharge signal andaddress signals, the precharge signal having been level-shifted.

Since the precharge signal is level-shifted before being supplied toeach row decoder, the row decoder need not incorporate a level-shiftingcircuit. Hence, the semiconductor memory device has fewer level-shiftingcircuits than the conventional semiconductor memory device. As a result,the devices can have a smaller chip size and can operate at a lowerpower consumption particularly for the boosted potential than theconventional semiconductor memory device.

The level-shifting of the precharge signal provides another advantage.Were each address signal level-shifted, a long time would elapse betweenthe generation of the signal and the input of the signal to the rowdecoder, inevitably decreasing the speed of the semiconductor memorydevice. In the case where the precharge signal is level-shifted as inthe memory device of this invention, it suffices to precharge ordischarge the row decoder in order to input the address signal to therow decoder. The address signal can be quickly input to the row decoder,enabling the memory device to operate at high speed.

The level-shifting circuits are susceptive to the influence of noisebecause of their structure. Where they are located close to thememory-cell region, where noise will likely be generated, they mightcause errors. Since they are arranged far from the memory-cell region inthe present invention, they are scarcely affected by the noise generatedin the memory-cell region, and therefore operate without causing errors.

To achieve the first object, according to a second aspect of the presentinvention a semiconductor memory device is provided in which a pluralityof row decoders and a plurality of partial decoders exist. The rowdecoders are connected to receive a precharge signal and addresssignals. The partial decoders are connected to receive a prechargesignal and address signals, which are different from those supplied tothe row decoders. The precharge signals are ones which have beengenerated by level-shifting a signal.

The semiconductor memory device according to the second aspect can havethe same advantages as the memory device according to the first aspect.

To achieve the second object described above, according to a thirdaspect of the invention a semiconductor memory device has a plurality ofrow decoders, a plurality of partial decoders and a plurality ofword-line noise killer circuits. The row decoders are connected toreceive a precharge signal and address signals. The partial decoders areconnected to receive a precharge signal and address signals, which aredifferent from those supplied to the row decoders. The precharge signalsare ones which have been generated by level-shifting a signal. Theword-line noise killer circuits are controlled by inverted signals whichare substantially the outputs of the partial decoders. The invertedsignals are generated by a circuit which is driven by the power-supplypotential, not by a boosted potential.

The semiconductor memory device according to the third aspect offers thesame advantages as the memory device according to the first aspect.Furthermore, it is advantageous in that the power required to generatethe boosted potential can be reduced since the circuit for generatingthe inverted signals is driven by the power-supply potential, not by aboosted potential.

To achieve the second object described above, according to a fourthaspect of the invention there is provided a semiconductor memory devicewhich comprises an array of memory cells, an array of word-line drivingcircuits and an array of word-line noise killer circuits. The array ofthe word-line noise killer circuits is arranged between the the array ofmemory cells and the array of the word-line driving circuits.

With this memory device, the word-line driving circuits can besufficiently spaced from the array of memory cells, without increasingthe chip size of the device. The noise interference between eachword-line driving circuit and the memory cell array can therefore besuppressed, minimizing the possibility that the memory device generateserrors.

To achieve the second object described above, according to a fifthaspect of the invention a semiconductor memory device is provided withan array of memory cells, a plurality of word-line driving circuits anda plurality of word-line noise killer circuits. The N-channel,gate-insulated FETs included in the word-line noise killer circuits havetheir gates extending at right angles to the gates of the P-channel,gate-insulated FETs and N-channel, gate-insulated FETs which areincorporated in the word-line driving circuits.

With the memory device according to the fifth aspect, the word lines canextend substantially straight, from the word-line driving circuits tothe array of memory cells. Because they are substantially straight, theword lines can be formed easily.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram showing conventional word-line selectingcircuits which are identical and incorporated in a semiconductor memory;

FIG. 2 is a circuit diagram illustrating another conventional word-lineselecting circuit for use in a semiconductor memory;

FIG. 3 is a block diagram showing the VPP-generating circuit,level-shifting circuit, word-line selecting circuits and memory cells,all incorporated in a dynamic RAM according to a first embodiment ofthis invention;

FIG. 4 is a circuit diagram of the word-line selecting circuits shown inFIG. 3;

FIG. 5 is a circuit diagram of the level-shifting circuit shown in FIG.3;

FIG. 6 is a circuit diagram of the VPP-generating circuit shown in FIG.3;

FIG. 7 is a circuit diagram showing a modification of the word-lineselecting circuits illustrated in FIG. 4;

FIG. 8 is a block diagram showing the VPP-generating circuit,level-shifting circuit, word-line selecting circuits and memory cells,all incorporated in a dynamic RAM according to a second embodiment ofthis invention;

FIG. 9 is a block diagram showing the level-shifting circuits, word-lineselecting circuits and partial decoders, all incorporated in a dynamicRAM according to a third embodiment of the invention;

FIG. 10 is a block diagram showing a dynamic RAM according to a fourthembodiment of the present invention;

FIG. 11 is a circuit diagram of one of the identical word-line selectingcircuits used in the dynamic RAM of FIG. 10;

FIG. 12 is a circuit diagram of the word-line drive-signal selectingcircuit shown in FIG. 10;

FIG. 13 is a diagram illustrating the chip layout of the dynamic RAMshown in FIG. 10;

FIG. 14 is a diagram showing the array of the word-line driving circuitsand the array of word-line noise killer circuits, both incorporated inthe dynamic RAM of FIG. 10;

FIG. 15A is a diagram showing the array of the word-line drive-signalcircuits and the array of the killer driving circuits;

FIG. 15B is a diagram showing the array of the word-line drive-signalcircuits and the array of the killer driving circuit;

FIG. 16 is a wiring-pattern diagram of a part of the dynamic RAM shownin FIG. 10;

FIG. 17 is a plan view of the memory cell array incorporated in thedynamic RAM of FIG. 10, showing the wiring-pattern of the memory cellarray;

FIG. 18 is a sectional view of a part of the memory cell array, showingtwo adjacent BPT cells included in the memory cell array;

FIG. 19 is a sectional view of the substrate of the dynamic RAM shown inFIG. 10, illustrating the array of word-line driving circuits, the arrayof word-line noise killer circuits and the memory cell array;

FIG. 20 is a diagram showing the chip layout of the memory block of thedynamic RAM shown in FIG. 10;

FIG. 21 is a circuit diagram illustrating a dynamic RAM according to afifth embodiment of the present invention; and

FIG. 22 is a circuit diagram showing a word-line selecting circuit of atype which can be incorporated in the dynamic RAM illustrated in FIG.21.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will now be described, with reference tothe accompanying drawings. In the drawings, identical reference numeralsdenote the same component, which will not be repeatedly explained in thefollowing description.

The present invention can be applied to various types of semiconductormemories, such as the dynamic RAM, the static RAM, the erasableprogrammable ROM, the mask ROM. Nonetheless, the invention isparticularly suitable for a dynamic RAM. Some dynamic RAMs will bedescribed below, which are embodiments of the present invention.

FIG. 3 shows a dynamic RAM according to a first embodiment of theinvention. More precisely, FIG. 3 is a block diagram showing aVPP-generating circuit 14, a level-shifting circuit 15, word-lineselecting circuits 16-0 to 16-n, and memory cells 10--all included inthe dynamic RAM.

As shown in FIG. 3, memory cells 10 are connected to each of word linesWL0 to WLn. The word-line selecting circuits 16-0 to 16-n are connectedto the word lines WL0 to WLn, respectively. Each word-line selectingcircuit has a row decoder (hereinafter referred to as "VPP-based rowdecoder) 13, a boosted potential supplying circuit (hereinafter referredto as "VPP-supplying circuit) 12 and a word-line driving circuit 11.

Each of the word-line driving circuits 11-0 to 11-n includes a P-channelMOS field-effect transistor (hereinafter referred to as "PMOSFET") 23.The drain of the PMOSFET 23 is connected to the word line WL. That is,the PMOSFETs 23-0 to 23-n have their drains connected to the word linesWL0 to WLn, respectively. The sources of the PMOSFETs 23-0 to 23-n areconnected to the VPP-supplying circuits 12-0 to 12-n, respectively. Thecircuits 12-0 to 12-n are connected to the VPP-generating circuit 14which is incorporated in the memory chip. The VPP-generating circuit 14generates a boosted potential VPP from the power-supply voltage VCCapplied to it. The boosted potential VPP is higher than the power-supplyvoltage VCC. Thus, the VPP-supplying circuits 12-0 to 12-n can supplythe boosted potential VPP to the sources of the PMOSFETs 23-0 to 23-n.

The VPP-supplying circuits 12-0 to 12-n may be replaced by lines. Ifthis is the case, the boosted potential VPP will be applied to thesources of the PMOSFETs 23-0 to 23-n as long as the dynamic RAMoperates. Alternatively, each VPP-supplying circuit 12 may include aswitching transistor, and a partial decoder may be connected to the gateof the switching transistor. In this case, the transistor will be turnedon when selected by the partial decoder, thereby applying the boostedpotential VPP to the source of the PMOSFET 23 used in the word-linedriving circuit 11.

The PMOSFETs 23-0 to 23-n have their gates connected to the VPP-basedrow decoders 13-0 to 13-n, respectively, and are controlled by thesignals output from the row decoders 13-0 to 13-n. A circuit elementsuch as an inverter may be provided between each VPP-based row decoder13 and the PMOSFET 23, in which case the PMOSFET 23 is controlled by asignal corresponding to the output signal of the row decoder 13. TheVPP-based row decoders 13-0 to 13-n are controlled is by a controlsignal, such as a precharge signal or an address signal. In the presentinvention, it is important that the control signal is a VPP-based onewhose high level is equal to the VPP level. The VPP-based control signalis a signal the level-shifting circuit 15 has generated by shifting aVCC-based control signal whose high level is equal to the VCC level.

In the dynamic RAM of FIG. 3, the control signal input to the VPP-basedrow decoders 13-0 to 13-n is a VPP-based one which the level-shiftingcircuit 15 has generated by converting a VCC-based control signal. Thedynamic RAM need not have a plurality of level-shifting circuits, eachprovided for one word-line selecting circuit, as in the circuitsillustrated in FIGS. 1 and 2. Only one level-shifting circuit isrequired to control a plurality of VPP-based row decoders 13-0 to 13-n.Therefore, the dynamic RAM of FIG. 3 can have a low chip size andoperate at small power dissipation.

In the dynamic RAM of FIG. 3, the level-shifting circuit 15 need not belocated in any word-line selecting circuit 16, unlike in the circuitsillustrated in FIGS. 1 and 2. Rather, the circuit 15 is positioned farfrom the memory cell array, which is likely to generate noise. Thelevel-shifting circuit 15 is scarcely affected by the noise generated bythe memory-cell array. The circuit 15 does not cause errors even if arelatively large noise is generated in the memory-cell array. On theother hand, as described above, the word-line selecting circuit maycause errors as do the circuits shown in FIGS. 1 and 2, because it mustbe provided near the memory-cell array due to the chip-elementarrangement. The higher the integration density of the memory, the moreinfluence the noise generated in the memory-cell region will have on thelevel-shifting circuit. The word-line selecting circuits of FIGS. 1 and2 are very likely to cause errors if incorporated in a 64-MB or 256-MBdynamic RAM.

The farther the level-shifting circuit 15 is located from the word-lineselecting circuits 16-1 to 16-n, the less the influence of the noisegenerated in the memory-cell region, but the longer the lines connectingthe circuit 15 to the word-line selecting circuits 16-0 to 16-n. Herearises a problem. The longer the lines, the greater their parasiticcapacitance, and the lower the operating speed of the word-lineselecting circuits 16-0 to 16-n. It is desirable that the memory-cellregion be arranged at one side of the substrate region in which thecircuits 16-0 to 16-n are provided, so as to shorten the word lines WL0to WLn as much as possible, thereby to prevent an increase in theparasitic capacitance of each word line. Also is it desirable that thelevel-shifting circuit 15 be arranged at another side (preferably theopposite side) of that substrate region and adjacent to the word-lineselecting circuits 16-0 to 16-n.

The word-selecting circuit region is arranged between the level-shiftingcircuit region and the memory-cell region in the dynamic RAM shown inFIG. 3. The level-shifting circuit 15 is therefore spaced apart from thememory cells 10 by the substrate region in which the word-line selectingcircuits 16-0 to 16-n are provided. The level-shifting circuit 15 isreliably prevented from being influenced by the noise generated in thememory-cell region. Furthermore, the lines connecting the circuit 15 tothe word-line selecting circuits 16-0 to 16-n are relatively short, notdecreasing the operating speed of the word-line selecting circuits 16-0to 16-n. In addition, the dynamic RAM can have a reduced chip size.

The VPP-generating circuit 14, the level-shifting circuit 15, theword-line selecting circuits 16-0 to 16-n and the memory cells 10--allincorporated in the dynamic RAM which is the first embodiment of thisinvention--will be described in greater detail with reference to FIGS.4, 5 and 6. FIG. 4 is a circuit diagram of the word-line selectingcircuits 16-0 to 16-n. FIG. 5 is a circuit diagram of the level-shiftingcircuit 15. FIG. 6 is a circuit diagram of the VPP-generating circuit14.

As shown in FIG. 4, memory cells 10 are connected to each of the wordlines WL0 to WLn. Each memory cell 10 is a dynamic RAM cell includingone transistor 21 and one capacitor 22. Each word line WL is connectedto the word-line driving circuit 11 (11-0, 11-1, . . . 11-n) included inthe word-line selecting circuit 16 (16-0, 16-1, . . . 16-n) provided forselecting the word line WL.

Each word-line selecting circuit 16 will be described. As can beunderstood from FIG. 4, the word-line driving circuit 11 includes aPMOSFET 23 (23-0, 23-1, . . . or 23-n) and an NMOSFET 24 (24-0, 24-1, .. . or 24-n). The drain of the PMOSFET 23 is connected to the drain ofthe NMOSFET 24. A boosted potential VPP is applied to the source of thePMOSFET 23, whereas a ground potential VSS is applied to the source ofthe NMOSFET 24. The line connecting the source of the PMOSFET 23 to theboosted potential VPP corresponds to the VPP-supplying circuit 12 whichis illustrated in FIG. 3. The gate of the PMOSFET 23 and the gate of theNMOSFET 24 are connected to each other. The node of the gates of theseMOSFETs 23 and 24 is connected to the output node a of the VPP-based rowdecoder 13.

The VPP-based row decoder 13 is connected at one end to the boostedpotential VPP and the ground potential VSS. It comprises a PMOSFET 26(26-0, 26-1, . . . 26-n) and a decoder circuit 29 (29-0, 29-1, . . .29-n) which are connected in series. The PMOSFET 26 is a prechargingtransistor, and the decode circuitly 29 is an NAND gate. The PMOSFET 26is controlled by a precharge signal PRCH', and the decode circuitly 29is controlled by controlled by row-address signals A0 to Ak orrow-address signals /A0 to /Ak. The row-address signals /A0 to /Ak havebeen obtained by inverting the signals A0 to Ak, respectively.) Theprecharge signal PRCH' is a VPP-based control signal which thelevel-shifting circuit 15 has generated by level-shifting a VPP-basedcontrol signal PRCH.

As shown in FIG. 4, each word-line selecting circuit 16 has a noisekiller circuit 17 (17-0, 17-1, . . . or 17-n). The noise killer circuit17 is connected to the output node a of the VPP-based row decoder 13.The circuit 17 comprises a load PMOSFET 28 (28-0, 28-1, . . . or 28-n)and an inverter 30 (30-0, 30-1, . . . 30-n). The PMOSFET 28 has itssource connected to the boosted potential VPP and its drain connected tothe output node a. The inverter 30 has its input terminal connected tothe boosted potential VPP and is designed to invert the potential levelat the output node a and apply it to the gate of the PMOSFET 28.

The level-shifting circuit 15 has the structure illustrated in FIG. 5.As can be understood from FIG. 5, the circuit 15 is designed to shiftthe level of the VPP-based control signal PRCH, thereby generating aprecharge signal PRCH'. The precharge signal PRCH', which is also aVPP-based control signal, is supplied to the PMOSFET 26 of the VPP-basedrow decoder 13, thus controlling the PMOSFET 26.

As shown in FIG. 6, the VPP-generating circuit 14 comprises a clocksignal generator 30, an inverter 31, a first voltage-raising capacitor32, a first MOSFET 33, a second MOSFET 34, a second voltage-raisingcapacitor 35, two other MOSFETs 24 and 27 and an output terminal 38. Theclock signal generator 30 generates a clock signal CP2, which issupplied to the inverter 31. The inverter 31 inverts the clock pulseCP2, generating a clock signal CP1 which is complementary to the clocksignal CP2. The clock signal CP1 is supplied to one end of the firstvoltage-boosting capacitor 32. The first MOSFET 33 is connected betweena terminal for applying the power-supply voltage VCC and the firstvoltage-boosting capacitor 32, and has its gate connected to receive theclock signal CP2 generated by the clock signal generator 30. The secondMOSFET 34 is connected between the terminal for applying thepower-supply voltage VCC and the second voltage-boosting capacitor 35,and has its gate connected to receive the clock signal CP1 generated bythe inverter 31. The MOSFET 24 has its drain and gate connected to thenode of the first MOSFET 33 and the first voltage-boosting capacitor 32.The source of the MOSFET 24 is connected to the output terminal 38. TheMOSFET 27 has its drain and gate connected to the node of the secondMOSFET 34 and the second voltage-boosting capacitor 35. The source ofthe MOSFET 27 is connected to the output terminal 38.

The VPP-generating circuit 14 is of the type which is generally used todrive the word lines of dynamic RAMs. It generates a boosted potentialVPP, which is supplied to the word-line selecting circuits 16-0 to 16-nthrough power-supply lines.

The operation of each word-line selecting circuit 16 will now beexplained, with reference to FIG. 4.

Before the row-address signals A0 to Ak or /A0 to /Ak are input to theNAND gate (decode circuitly) 29, the precharge signal PRCH', i.e., aVPP-based control signal, is changed within a predetermined time, i.e.,a precharging time, from the high level to the low level, and back tothe high level. To be more precise, the signal PRCH' is changed from theVPP level to the VSS level, and back to the VPP level. The PMOSFET 26 isturned on when the signal PRCH' changes to the VSS level, and is turnedoff after the output node a is charged to the VPP level.

The PMOSFET 28 prevents the potential level at the output node a fromchanging due to noise or the like, when the PMOSFET 26 is turned off,temporarily setting the output node a in a floating state. The inverter30, whose output is connected to the gate of the PMOSFET 28, includes aPMOSFET and an NMOSFET which are connected in series between the boostedpotential VPP and the ground potential VSS. The boosted potential VPP isused as the power-supply voltage of the inverter 30, for the followingreason. Were the boosted potential VPP replaced by the power-supplyvoltage VCC, the PMOSFET incorporated in the inverter 30 could not beturned off completely when the output node a is at the high potentiallevel. Should this happen, the inverter would fail to operate reliably,making it difficult to drive the word line WL at sufficiently highspeed.

After the lapse of the predetermined time (i.e., the precharging time),the address signals A0 to Ak or /A0 to /Ak are input, in a particularcombination, to the NAND gate 29. Then, only the output node a is set atthe VSS level if the word line WL connected to the word-line drivingcircuit 11 has been selected. The PMOSFET 23 is turned on, whereas theNMOSFET 24 is turned off. As a result, the potential of the word line WLselected rises to the VPP level. The transistors 21 of the memory cells10 connected to the word line WL are turned on. The data stored in thecapacitors 22 of the memory cells 10 is thereby transferred to the bitlines (not shown) of the dynamic RAM.

Assume that the word line WL connected to the word-line driving circuit11 has not been selected. In this case, the output node a remains at theVPP level. The PMOSFET 23 is turned off, whereas the NMOSFET 24 isturned on. The potential of the word line WL not selected does not riseto the VPP level. Consequently, no data is read from the memory cells10.

The NMOSFET 24 is on while the word line WL remains unselected, so as tofix the potential of the word line at zero level. Namely, the NMOSFET 24prevents the word line WL from assuming a floating state. Hence, theword line WL is reliably prevented from being selected erroneously evenif its potential varies due to noise.

Of the signals for controlling the VPP-based row decoder 13, only theprecharge signal PRCH', which is a VPP-based control signal, has beengenerated by level-shifting the precharge control signal PRCH and issupplied to the PMOSFET 26 of the VPP-based row decoder 13. Therow-address signals A0 to Ak or /A0 to /Ak, which are supplied to thegates of the NMOSFETs constituting the NAND gate 29 are VCC-basedcontrol signals, unlike the precharge signal PRCH'. This is because anysignal for controlling a PMOSFET must be a VPP-based control signal,while any signal for controlling an NMOSFET need not be a VPP-basedcontrol signal. An PMOSFET cannot be turned off completely whencontrolled by a VCC-based signal which is at its high level (i.e., theVCC level). By contrast, an NMOSFET is completely turned off whencontrolled by a VCC-based signal which is at its low level (i.e., theVSS level).

Needless to say, the NMOSFETs of the NAND gate 29 may be controlled byVPP-based control signals, causing no malfunction of the VPP-based rowdecoder 13. In other words, all signals controlling the word-lineselecting circuit 16 can be VPP-based control signals. It is necessary,however, to use VPP-based signals to control at least the PMOSFETsincorporated in the word-line selecting circuit 16.

As mentioned above, the PMOSFET 26 of the row decoder 13 is used as aprecharging transistor. This is because the threshold voltage of aPMOSFET hardly decrease, while that of an NMOSFET is likely to decrease.Thus, the PMOSFET 26 effectively functions as a precharging transistor.

In the dynamic RAM illustrated in FIG. 3, at least one of the signalscontrolling each word-line selecting circuit 16 (e.g., the signalcontrolling any PMOSFET) must be a VPP-based control signal. How theVPP-based control signal should be generated is not essential.

The dynamic RAM shown in FIG. 3 needs only one level-shifting circuit,i.e., the circuit 15. For level-shifting the precharge control signalPRCH, thereby to generate the precharge signal PRCH' which is aVPP-based control signal. As many level-shifting circuits as theword-line selecting circuits need not be used as in the conventionalsemiconductor memory which has the word-line selecting circuits of thetype shown in FIG. 1 or FIG. 2. Requiring only one level-shiftingcircuit, the dynamic RAM of FIG. 3 can have a smaller chip size andoperate at lower power consumption than the conventional semiconductormemory. Moreover, the dynamic RAM can operate reliably, making virtuallyno errors, as has been explained with reference to FIG. 3.

In the dynamic RAM shown in FIG. 3, each word-line selecting circuit 16requires only two power supplies, i.e., the boosted potential VPP andthe ground potential VSS. It does not need the potential VCC since noVCC lines are formed in the substrate region where the word-lineselecting circuit is formed. In this substrate region there is providedonly two power-supply lines, i.e., a VSS line and a VPP line. The VSSline and the VPP lines can be made broader than in the case where a VCCline is formed also in that substrate region. If the VSS line and theVPP line have a sufficient width, their potential levels can beprevented from varying due to noise or the like. In addition, it wouldbe easier to design the circuit configuration than in the case where aVCC line is provided also in that substrate region, in addition to theVSS line and the VPP line.

In each word-line selecting circuit 16, the output node a of theVPP-based row decoder 13 is connected directly to the gate of thePMOSFET 23 and that of the NMOSFET 24, both included in the word-linedriving circuit 11. Alternatively, the node a may be connected to thegates of the MOSFETs 23 and 24 by means of a plurality of VPP-basedinverters. This connection scheme can be employed in other embodiments,which will be described below.

FIG. 7 shows a modified word-line selecting circuit in which theVPP-based row decoder 13 is not directly connected to the gate of thePMOSFET 23 incorporated in the word-line driving circuit 11, butconnected thereto by two VPP-based inverters 18 (18-0, 18-1, . . . 18-n)and 19 (19-0, 18-1, . . . 18-n). These inverters 18 and 19 are providedfor controlling the timing of controlling the PMOSFET 23.

It does not matter whether the row decoder 13 and the word-line drivingcircuit 11 are directly connected as shown in FIG. 4, or indirectlyconnected by inverters or the like as illustrated in FIG. 7. In eitherconnection scheme, the PMOSFET 23 and the NMOSFET 24, both provided fordriving the word line WL, can be controlled in accordance with thepotential at the output node a of the VPP-based row decoder 13.

FIG. 8 shows a dynamic RAM according to a second embodiment of thepresent invention. To be more specific, FIG. 8 is a block diagramshowing a VPP-generating circuit 14, a level-shifting circuit 15,word-line selecting circuits 16-0 to 16-n, and memory cells 10--allincorporated in this dynamic RAM.

In the dynamic RAM shown in FIG. 3, i.e., the first embodiment, theVPP-supplying circuits 12-0 to 12-n are used in the word-line selectingcircuits 16-0 to 16-n, respectively. In the dynamic RAM shown in FIG. 8,i.e., the second embodiment, only one VPP-supplying circuit 12 isprovided for supplying the boosted potential VPP to all word-lineselecting circuits 16-0 to 16-n.

In the dynamic RAMs illustrated in FIGS. 3 and 8 (i.e., the first andsecond embodiments of the present invention), one level-shifting circuit15 shifts the level of the precharge control signal PRCH, thusgenerating the precharge signal PRCH'. Instead, a plurality oflevel-shifting circuits which perform exactly the same operation may beused to shift the level of one and the same control signal, inconsideration of the parasitic capacitance of lines and the drivingability of each level-shifting circuit. For example, level-shiftingcircuits may be provided for memory-cell blocks, or for groups ofmemory-cell blocks, respectively. This design scheme can be applied toother embodiments which will be described below.

FIG. 9 shows a dynamic RAM according to a third embodiment of thispresent invention. More specifically, FIG. 9 is a block diagramillustrating level-shifting circuits 15-1 and 15-2, word-line selectingcircuits 16A-0 to 16A-n and partial decoders 40a to 40d--allincorporated in this dynamic RAM.

The dynamic RAM shown in FIG. 9 is a partial-decode type one. A dynamicRAM of partial-decode type can be operated with a low voltage because arelatively small number of transistors are connected in series betweenthe power-supply potentials. It is therefore considered suitable for useas a semiconductor memory having a large memory capacity.

The dynamic RAM according to the third embodiment differs from thedynamic RAMs shown in FIGS. 3 and 8 (i.e., the first and secondembodiments) in that four partial decoders 40a to 40d are used in placeof the VPP-supplying circuits 12-0 to 12-n (FIG. 3) or the singleVPP-supplying circuit 12 (FIG. 8). The decoders 40a to 40d perform afunction called "partial decoding" or "pre-decoding."

The partial decoders 40a to 40d are connected to receive a VPP-levelsignal which the second level-shifting circuit 15-2 has generated bylevel-shifting a second control signal at the VCC level. The partialdecoders 40a to 40d generate word-line driving signals WDRV1 to WDRV4from the VPP-level signal. The driving signals WDRV1 to WDRV4, each atthe VCC level, are supplied to each word-line selecting circuit 16A.Each word-line selecting circuit 16A differs a little from itscounterpart 16 incorporated in the dynamic RAMs shown in FIGS. 3 and 8.More precisely, it has four word-line driving circuit 11a to 11d whichare connected to the partial decoders 40a to 40d in order to receive thedriving signals WDRV1 to WDRV4, respectively.

The word-line driving circuit 11a includes a PMOSFET 23a which has itsgate connected to the output node a of a main row decoder 13, its sourceconnected to the output node b of the partial decoder 40a, and its drainconnected to the word line WL1. Similarly, the word-line driving circuit11b includes a PMOSFET 23b which has its gate connected to the outputnode a of a main row decoder 13, its source connected to the output nodeb of the partial decoder 40b, and its drain connected to the word lineWL2. The word-line driving circuit 11c includes a PMOSFET 23c which hasits gate connected to the output node a of a main row decoder 13, itssource connected to the output node b of the partial decoder 40c, andits drain connected to the word line WL3. The word-line driving circuit11d incorporates a PMOSFET 23d which has its gate connected to theoutput node a of a main row decoder 13, its source connected to theoutput node b of the partial decoder 40d, and its drain connected to theword line WL4.

As indicated above, the dynamic RAM has a plurality of word-lineselecting circuits 16A-0 to 16A-n, as does any dynamic RAM ofpartial-decode type. Each word-line selecting circuit 16A includes onemain row decoder 13. Thus, the dynamic RAM has main row decoders 13-0 to13-n in all. Supplied to each main row decoder 13 are a VPP-levelcontrol signal which the first level-shifting circuit 15-1 has generatedby level-shifting a first control signal at the VCC level, as in thedynamic RAMs according to the first and second embodiment.

In a conventional semiconductor memory of partial-decode type, eachword-line selecting circuit and each partial decoder need to have onelevel-shifting circuit each. The conventional memory inevitablycomprises a relatively large number of circuits. This means that theconventional memory has a very large number of transistors. By contrast,the dynamic RAM according to the third embodiment of the invention needsonly two level-shifting circuits, i.e., the first level-shifting circuit15-1 which generates the VPP-level signal for controlling the main rowdecoders 13-0 to 13-n, and the second level-shifting circuit 15-2 whichgenerates the VPP-level signal for controlling the partial decoders 40ato 40d. The the dynamic RAM shown in FIG. 9 has less circuits than theconventional semiconductor memory. Hence, it has far less transistors,and can have a small chip size and a high integration density, as do thedynamic RAMs according to the first and second embodiments. The use ofonly two level-shifting circuits results in a reduction of powerconsumed to generate boosted potential VPP.

The third embodiment is also advantageous in that the word lines WL1 toWLm are selected at higher speed than in a conventional semiconductormemory.

Each word-line selecting circuit incorporated in the conventional memoryhas a boot-strap circuit comprised a word-line driving NMOSFET and anisolation MOSFET. The isolation MOSFET is used to suppress a reverseflow of carries from the gate of the word-line driving NMOSFET. Theoutput of a partial decoder is supplied to the source of the NMOSFET tocouple the gate and source of the NMOSFET. To prevent the thresholdvoltage of the NMOSFET from decreasing, the output of the partialdecoder must be supplied after the main row decoder has generated aoutput and the gate of the NMOSFET has thereby been chargedsufficiently. It is necessary to delay the outputting of a word-linedriving signal WDRV to the NMOSFET. As a consequence, the word lines areselected but at low speed.

In the dynamic RAM shown in FIG. 9, PMOSFETs are used as word-linedriving transistors. The threshold voltage of each PMOSFET hardlydecreases. It is not necessary to supply a precharge signal PRCH2' tothe partial decoders 40a to 40d after lapse of a predetermined time fromthe supplying of a precharge signal PRCH1' to the main row decoder 13.Rather, the signal PRCH2' can be supplied to the partial decoders 40a to40d at the same time the signal PRCH1' is supplied to the main rowdecoder 13. Hence, the word lines WL1 to WLm can be selected at higherspeed than in a conventional semiconductor memory.

FIG. 10 shows a dynamic RAM according to a fourth embodiment of theinvention, which is similar to the dynamic RAM according to the thirdembodiment.

As can be understood from the block diagram of FIG. 10, a prechargesignal generating circuit 1 generates a VCC-level precharge signal PRCHwhich is used to precharge and discharge main row decoders 13-0 to 13-7and partial decoders 40a to 40d. The precharge signal PRCH is suppliedto a level-shifting circuit 15. The circuit 15 shifts the level of theprecharge signal PRCH, generating a first precharge signal PRCH1' and asecond precharge signal PRCH2' which are at VPP level. The firstprecharge signal PRCH1' is input directly to the main row decoders 13-0to 13-7, and the second precharge signal PRCH2' to the partial decoders40a to 40d. Instead, the signal PRCH1' may be supplied to the main rowdecoders via a buffer circuit including an inverter, and the signalPRCH2' may be supplied to the partial decoders through a buffer circuitincluding an inverter. This method of supplying the precharge signalsmay be employed in the case where the signals PRCH1' and PRCH2' must beinput to the main row decoders and the partial decoders at differenttimes, or the signals PRCH1' and PRCH2' must have different currentdrivabilities.

As shown in FIG. 10, the dynamic RAM has eight word-line selectingcircuits 16A-0 to 16A-7 and four drive-signal line selecting circuits39a to 39d. Each word-line selecting circuit 16A has one main rowdecoder 13, and each drive-signal line selecting circuit 39 has onepartial decoder 40. It follows that the dynamic RAM has eight main rowdecoders 13-0 to 13-7 and four partial decoders 40a to 40d.

The first precharge signal PRCH1', which has been generated bylevel-shifting the precharge signal PRCH, is supplied to the main rowdecoders 13-0 to 13-7. Three of six row-address signals A3, A4, A5, /A3,/A4 and /A5 are input to each main row decoder 13. Eight combinations ofrow-address signals, each consisting of three signals, are thereforesupplied to the main row decoders 13-0 to 13-7, respectively.

Each of the word-line selecting circuits 16A-0 to 16A-7 comprises a mainrow decoder 13, an output line a, four partial output lines aa to ad,four word-driving circuits 11a to 11d, and four word-line noise killercircuits 41a to 41d. The output line a is connected at one end to themain row decoder 13 and at the other end to the partial output lines aato ad. The partial output lines aa to ad are connected to the word-linedriving circuits 11a to 11d. The circuits 11a to 11d are coupled to thenoise killer circuits 41a to 41d, which in turn are are connected tofour word lines WL.

The second precharge signal PRCH2', which has been generated bylevel-shifting the precharge signal PRCH, is supplied to the partialdecoders 40a to 40d which are incorporated in the drive-signal lineselecting circuits 39a to 39d. Two of four row-address signals A0, A1,/A0 and /A1 are input to each main row decoder 13. Thus, fourcombinations of row-address signals, each consisting of two signals, aresupplied to the partial decoders 40a to 40d, respectively.

In the fourth embodiment (FIG. 10), four different row-address signalsare available which can be input to the partial decoders 40a to 40d.Alternatively, six different row-address signals may be used. If this isthe case, there will be eight combinations of row-address signals, andeight partial output lines, instead of four, will be provided in eachword-line selecting circuit 16A.

A pair of lines are connected to the drive-signal line selecting circuit39a, for supplying word-line driving signals WDRV1 and /WDRV1. Theword-line driving circuits 11a-0 to 11a-7 are arranged at theintersections of the line for supplying the word-line driving signalWDRV1 and the partial output lines aa of the word-line selectingcircuits 16A-0 to 16A-7. As clearly shown in FIG. 10, the otherword-line driving circuits 11b-0 to 11b-7, 11c-0 to 11c-7, 11d-0 to11d-7 are arranged in a similar fashion. The word-line noise killercircuits 41a-0 to 41a-7 are arranged at the intersections of the linefor supplying the word-line driving signal /WDRV1 and the partial outputlines aa of the word-line selecting circuits 16A-0 to 16A-7. As shown inFIG. 10, the other word-line noise killer circuits 41b-0 to 41b-7, 41c-0to 41c-7, 41d-0 to 41d-7 are arranged in a similar manner.

The word-line selecting circuits 16A-0 to 16A-7 are identical in termsof structure. The word-line selecting circuit 16A-0 will be described indetail, with reference to FIG. 11.

As FIG. 11 shows, the word-line selecting circuit 16A-0 is similar tothose incorporated in the first embodiment and illustrated in FIG. 4. Itdiffers in that the output line a is connected to four partial outputlines aa, ab, ac and ad. The word-line driving circuits 11a-0 to 11d-0have almost the same structure as those shown in FIG. 4, but word-linedriving signals WDRV1 to WDRV4 are supplied to the sources of PMOSFETs23a-0 to 23d-0, respectively. The signals WDRV1 to WDRV4, which are atthe VPP level, energize the word-line driving circuits 11a-0 to 11d-0.The outputs of the word-line driving circuits 11a-0 to 11d-0 areconnected to the word lines WL1 to WL4. Connected to the word lines WL1to WL4 are the word-line noise killer circuits 41a-0 to 41d-0. Theword-line noise killer circuits include NMOSFETs 42a-0 to 42d-0,respectively. These NMOSFETs have their drains connected to the wordlines WL1 to WL4. Inverted word-line driving signals /WDRV1 to /WDRV4are input to the gates of the NMOSFETs 42a-0 to 42d-0. Each of theseNMOSFETs is turned on when the input signal /WDRV is at the high level,setting the potential of the word line WL at the VSS level.

Assume that the word-line noise killer circuits 41a-0 to 41d-0 are notprovided. Even so, the potential of the word WL can remain at the lowlevel when the output of the main row decoder 13-0 and the word-linedriving signal WDRV are at the low level. In practice, however, thepotential of the word WL inevitably varies due to noise or the like,between ov and a threshold voltage Vth. It is quite possible that eachword-line driving circuit makes errors.

As indicated above, the NMOSFET incorporated in each word-line noisekiller circuit is turned on when the inverted word-line driving signal/WDRV is at the high level--that is when the word-line driving signalWDRV is at the low level. The potential of the word line WL is therebyfixed at the VSS level. This suppresses variation of the potential atthe word line WL, despite noise or the like. In the present embodiment,the inverted word-line driving signals /WDRV1 to /WDRV4 are set at theVCC level. Nonetheless, the signals /WDRV1 to /WDRV4 may be set at theVPP level as the word-line driving signals WDRV1 to WDRV4.

The drive-signal line selecting circuits 39a to 39d are identical instructure. The drive-signal line selecting circuit 39a will be describedin detail, with reference to FIG. 12.

As FIG. 12 shows, the drive-signal line selecting circuit 39aincorporates the partial decoder 40a. The partial decoder 40a is similarto the main row decoder 13-0 (FIG. 11) in structure. The output line cof the partial decoder 40a is connected to a drive-signal line drivingcircuit 43a. Connected to the output line c is a noise killer circuit44a which is similar in structure to the noise killer circuit 17-0illustrated in FIG. 4.

The drive-signal line driving circuit 43a has a PMOSFET 45a and anNMOSFET 46a. The PMOSFET 45a has its source connected to a boostedpotential VPP, its drain coupled to an output line b and its gateconnected to the output line c. The NMOSFET 46a has its source connectedto a low potential VSS, its drain connected to the output line b and itsgate coupled to the output line c. The circuit 43a generates theword-line driving signal WDRV1, which is output through the output lineb.

Connected to the output line b is a killer-driving circuit 47a which isdesigned to drive the word-line noise killer circuit 41a-0. Thekiller-driving circuit 47a includes an inverter which inverts theword-line driving signal WDRV1, thereby producing the word-line drivingsignal /WDRV1. The inverter comprises a PMOSFET 48a and an NMOSFET 49a.The PMOSFET 48a has its source coupled to a high potential VCC, itsdrain connected to an output line d and its gate connected to the outputline b. The NMOSFET 49a has its source connected to the low potentialVSS, its drain coupled to the output line d and its gate coupled to theoutput line b. The killer-driving circuit 47a generates the word-linedriving signal /WDRV1, which is output through the output line d.

The inverter incorporated in the killer-driving circuit 47a utilizes thehigh potential VCC as input power. Therefore, power consumed to generateboosted potential VPP can be reduced. The inverter may be replaced by aninverter which uses the boosted potential VPP as input power. In thiscase, the potential of the word line WL can be quickly changed to theVSS level, whereby the word line WL is driven at high speed, and theline for applying the high potential VCC can be omitted.

For a memory having a large storage capacity it is desirable to minimizethe power consumed to generate boosted potential VPP. The smaller thepower used to generate boosted potential VPP, the less the VPPfluctuation, and the smaller a potential-boosted capacitor.

The drive-signal line selecting circuits 39a to 39d may be of the samestructure as the modified word-line selecting circuit which isillustrated in FIG. 7.

The dynamic RAM according to the fourth embodiment needs to have onelevel-shifting circuit only. The level-shifting circuit 15 shifts thelevel of the precharge signal PRCH and generates two precharge signalsPRCH1' and PRCH2'. The signal PRCH1' is input to the main row decoders13-0 to 13-7, and the signal PRCH2' to the partial decoders 40a to 40d.Having only one level-shifting circuit, the dynamic RAM comprises lesscircuits and, hence, far less transistors than the conventionalsemiconductor memory.

Furthermore, since only one level-shifting circuit is used, powerrequired to generate boosted potential VPP can be reduced more than inthe third embodiment (FIG. 9) which has two level-shifting circuits,i.e., the circuit 15-1 for generating a VPP-level signal to control themain row decoders 13-0 to 13-n and the circuit 15-2 for generating aVPP-level signal to control the partial decoders 40a to 40d.

As indicated above, the inverted word-line driving signal /WDRV1 isgenerated by an inverter which uses the high potential VCC as power.This also helps to decrease power consumed to generate boosted potentialVPP.

The chip layout of the dynamic RAM according to the fourth embodimentwill be described. The components of the dynamic RAM are arranged in anovel and useful pattern which increases the integration density,facilitates the manufacture and suppresses noise interference.

FIG. 13 is a diagram illustrating the chip layout of the dynamic RAM. AsFIG. 13 shows, the RAM has an array 100 of memory cells, an array 101 ofword-line driving circuits, an array 102 of word-line noise killercircuits, an array 103 of drive-signal line driving circuits, and anarray 104 of killer-driving circuits.

The array 100 comprises memory cells arranged in rows and columns.

The array 101 includes the PMOSFETs 23a-0 to 23a-7, 23b-0 to 23b-7,23c-0 to 23c-7 and 23d-0 to 23d-7, and the NMOSFETs 24a-0 to 24a-7,24b-0 to 24b-8, 24c-0 to 24c-7 and 24d-0 to 24d-7, which areincorporated in the word-line driving circuits and which are arranged ina prescribed pattern.

The array 102 of word-line noise killer circuits is arranged between thearray 100 of memory cells and the array 101 of word-line drivingcircuits. The array 102 includes the NMOSFETs 42a-0 to 42a-7, 42b-0 to42b-7, 42c-0 to 42c-7 and 42d-0 to 42d-7, which are used in theword-line noise killer circuits and which are arranged in a specificpattern.

The array 103 of drive-signal line driving circuits is located adjacentto the array 101 of word-line driving circuits. More precisely, thearray 103 consists of two sub-arrays 103-1 and 103-2, which arepositioned on two opposite sides of the array 101, respectively. Thefirst sub-array 103-1 includes the PMOSFETs 45a and 45c and the NMOSFETs46a and 46c which are used in the drive-signal line driving circuit. Thesecond sub-array 103-2 includes the PMOSFETs 45b and 45d and theNMOSFETs 46b and 46d which are included in the drive-signal line drivingcircuit.

The array 104 of killer-driving circuits is provided adjacent to the 102of word-line noise killer circuits. To be more specific, the array 104consists of two sub-arrays 104-1 and 104-2, which are positioned on twoopposite sides of the array 102, respectively. The first sub-array 104-1includes the PMOSFETs 48a and 48c and the NMOSFETs 49a and 49c which areincorporated in the killer-driving circuit. The second sub-array 104-2includes the PMOSFETs 48b and 48d and the NMOSFETs 49b and 49d which areused in the killer-driving circuit.

FIG. 14 is a diagram showing, in detail, the array 101 of word-linedriving circuits and the 102 of word-line noise killer circuits. FIG.15A is a diagram illustrating, in detail, the first sub-array 103-1 ofdrive-signal line driving circuits and the first sub-array 104-1 ofkiller-driving circuits. FIG. 15A is a diagram depicting, in detail, thesecond sub-array 103-2 of drive-signal line diving circuits and thesecond sub-array 104-2 of killer-driving circuits.

The arrays 101 and 102 will be described in detail, with reference toFIG. 14. As shown in FIG. 14, the NMOSFETs 42a-0 to 42a-7, 42b-0 to42b-7, 42c-0 to 42c-7 and 42d-0 to 42d-7 used in the word-line noisekiller circuits are oriented at 90° with respect to the PMOSFETs 23a-0to 23a-7, 23b-0 to 23b-7, 23c-0 to 23c-7 and 23d-0 to 23d-7 and theNMOSFETs 24a-0 to 24a-7, 24b-0 to 24b-7, 24c-0 t 24c-7 and 24d-0 to 24-7which are incorporated in the word-line driving circuits. Each arrowshown in FIG. 14 indicates the direction in which a current flowsthrough the corresponding MOSFET, and in which the gate of the MOSFETextends.

The sub-arrays 103-1, 103-2, 104-1 and 104-2 will be described in detailwith reference to FIGS. 15A and 15B. As shown in FIGS. 15A and 15B, thePMOSFETs 45a to 45d and the NMOSFETs 46a to 46d, which are used in thedrive-signal line driving circuits, are oriented in the same directionas the NMOSFETs 42a-0 to 42a-7, 42b-0 to 42b-7, 42c-0 to 42c-7 and 42d-0to 42d-7 included in the word-line noise killer circuits. Similarly, thePMOSFETs 48a to 48d and the NMOSFETs 49a to 49d, which are used in thekiller-driving circuits, are oriented in the same direction as theNMOSFETs 42a-0 to 42a-7, 42b-0 to 42b-7, 42c-0 to 42c-7 and 42d-0 to42d-7 which are included in the word-line noise killer circuits. Eacharrow shown in FIGS. 15A and 15B indicates, as those in FIG. 14, thedirection in which a current flows through the corresponding MOSFET, andin which the gate of the MOSFET extends.

As described above and shown in FIG. 13, the array 102 of word-linenoise killer circuits is arranged between the array 100 of memory cellsand the array 101 of word-line driving circuits. Thus, the array 101 ofword-line driving circuits is spaced far away from the array 100 ofmemory cells. The noise interference between the arrays 100 and 101 issuppressed, decreasing the possibility that the dynamic RAM make errorswhile operating.

As mentioned above and evident from FIGS. 14, 15A and 15B, the NMOSFETsincluded in the word-line noise killer circuits are oriented at 90° withrespect to the PMOSFETs and NMOSFETs which are included in the word-linedriving circuits. This prevents an increase in the substrate-surfacearea occupied by the word-line noise killer circuits. In other words,the dynamic RAM according to the fourth embodiment of the invention canhave a high integration density.

With the chip layout of FIG. 13 it is possible to arrange the word linesover the array 102 of word-line noise killer circuits--extending fromthe word-line driving circuits to the array 100 of memory cells as isillustrated in FIG. 16. That is, the word lines can extend straight.Straight word lines, though very thin, can be formed more easily thanword lines which are equally thin and bent at several portions.

FIG. 17 is a plan view of the array 100 of memory cells, incorporated inthe dynamic RAM (FIG. 10). As show n in FIG. 17, the array 100 comprisesmemory cells 200, each including one transfer transistor and onecapacitor. The transfer transistors of the cells 200 are oriented at 90°to the NMOSFETs incorporated in the word-line noise killer circuits. Thememory cells 200 are buried-plate trench (BPT) cells which can be formedin a high density.

FIG. 18 is a sectional view showing adjacent two of the BPT cells 200.As can be understood from FIG. 18, a plate potential VPL is applied tothe capacitor 201 of each BPT cell 200 from an N-type silicon layer 202provided within the P-type silicon substrate. The layer 202 has beenformed by diffusing an N-type impurity from the bottom of a trench 203made in the substrate. The layer 202 is buried in the substrate and isthus known also as "buried wiring layer."

The chip layout of FIG. 13 comes to have an advantage after the BPTcells 200 are formed in the memory cell region. This advantage will beexplained with reference to FIG. 19 which is a sectional view of thesubstrate, illustrating the array 101 of word-line driving circuits, thearray 102 of word-line noise killer circuits and the array 100 of memorycells.

As shown in FIG. 19, each BPT cell 200 has an N-type buried wiring layer202. The plate potential VPL is applied to the buried wiring layer 202.(Usually, the potential VPL is about half the power-supply potentialVCC.) The array 101 of word-line driving circuits has an N-type well inwhich PMOSFETs are formed. It is to the N-type well that the boostedpotential VPP is applied. Were the N-type well located close to theN-type buried wiring layer 202, the potential of the layer 202 wouldfluctuate due to the potential of the N-type well. As shown in FIG. 19,the array 102 of word-line noise killer circuits is provided between thearray 100 of memory cells and the array 101 of the word-line drivingcircuits. The array 102 isolates the N-type well from the N-type buriedwiring layer 202. The fluctuation in the potential of the layer 202 istherefore suppressed.

FIG. 20 is a diagram showing the chip layout of the memory block of thedynamic RAM according to the fourth embodiment of the invention. Asillustrated in FIG. 20, the array 105 of main row decoders is providedadjacent to the array 101 of word-line driving circuits. The array 106of partial decoders consists of two sub-arrays 106-1 and 106-2. Thefirst sub-array 106-1 is positioned close to the first sub-array 103-1of drive-signal line driving circuits, and the second sub-array 106-2adjacent to the second sub-array 103-2 of drive-signal line drivingcircuits. The region 107 of the level-shifting circuit 15 (FIG. 10) isarranged near the array 105 of main row decoders. The region capacitor108 is located adjacent to the region 109 of VPP-generating circuits.

In the chip layout shown in FIG. 20, the array 105 of main row decoders,the second sub-array 106-2 of partial decoders, the array 101 ofword-line driving circuits, and the array 102 of word-line noise killercircuits are arranged between the array 100 of memory cells and theregion 107 of the level-shifting circuit 15. Therefore, the noiseinterference between the level-shifting circuit 15 and the array 100 ofmemory cells can be suppressed. Further, since the region 107 of thelevel-shifting circuit 15 is provided near the array 105 of main rowdecoders, the distance between the circuit 15 and the main row decodersis short, and the lines connecting the circuit 15 to the main rowdecoders are short. The precharge signal PRCH1' can therefore besupplied from the level-shifting circuit 15 to the main row decoders13-0 to 13-7 without any noticeable delay. Still further, since bothsub-arrays 106-1 and 106-2 of partial decoders are located close to thearray 105 of main row decoders, the distance between the level-shiftingcircuit 15 and the partial decoders 40a to 40d is short, too.

In practice, a plurality of identical memory blocks of the type shown inFIG. 20 are integrated in a single semiconductor chip, thus constitutinga memory of a great storage capacity. Each of the memory blocksincorporates one capacitor region 108 and one region 109 ofvoltage-raising circuits. As a result, in each memory block there can begenerated a boosted potential VPP which scarcely varies. It should benoted that a variation of the potential VPP is a cause of malfunction ofthe dynamic RAM.

FIG. 21 is a circuit diagram illustrating a dynamic RAM according to afifth embodiment of the present invention. Like the third and fourthembodiments, the fifth embodiment is a dynamic RAM of partial-decodetype but differs in three respects. First, the row decoders arecomprised of CMOS circuits. Second, no precharge signals are used.Third, no noise killer circuits are connected to the output lines of therow decoders.

As is illustrated in FIG. 21, each VPP-supplying circuit 51 includes aPMOSFET 23 and an NMOSFET 24. The PMOSFET 23 and the NMOSFET 24 areconnected to one word line WL for driving the word line WL. The MOSFETs23 and 24 have their gates connected to each other. The node of theirgates is directly connected to the output line a of the VPP-based rowdecoder 50. Needless to say, the gate node may be connected to theoutput line aa by a VPP-based inverter, which delays the output signalof the decoder 50.

The row decoder 50 comprises a CMOS-NAND gate which is controlled byaddress signals A2 to A4. Each VPP-supplying circuit 51 further includesa partial decoder section comprised of a CMOS-NAND gate which iscontrolled by address signals A0 and A1. Both the row decoder 50 and thepartial decoder section are driven by a boosted potential VPP. Theaddress signals A0 to A4 control the PMOSFETs incorporated in the rowdecoder 50 and the VPP-supplying circuit 51. They must be VPP-basedcontrol signals so that the PMOSFETs may be turned off completely whenthe address signals are at high level. Each address signal is aVPP-based one which a level-shifting circuit (not shown) has generatedby level-shifting a VCC-based control signal. Thus, at least fivelevel-shifting circuits must be incorporated in the dynamic RAM shown inFIG. 21. If each level-shifting circuit has an inadequate drivability,one or more additional level-shifting circuits may be used to generate aVPP-based address signal.

Even if two or more level-shifting circuits are provided to generateeach VPP-based address signal, the fifth embodiment requires but farless level-shifting circuits than the conventional semiconductormemories. Like the first to fourth embodiment, the fifth embodiment canhave a low chip size and can operate at small power consumption and withhigh reliability, making virtually no errors.

Furthermore, the dynamic RAM according to the fifth embodiment isadvantageous in that the word lines can be driven at high speed. This isbecause any decoder circuit used in the fifth embodiment is a CMOScircuit, not a circuit comprised of NMOSFETs. It is thereforeunnecessary to input a precharge signal to charge the output of thedecoder circuit before the address signals are input to the decodercircuit. In addition, the potential at the output line a of any decoderhardly change the fact that a noise killer circuit is not connected tothe line a. This is because the output of the decoder is fixed at eitherthe VPP level or the VSS level and would not assume a floating state.

The technique of level-shifting a precharge signal cannot be applied tothe dynamic RAM according to the fifth embodiment. With the fifthembodiment, however, it is possible to drive noise killer drivingcircuits with the power-supply potential VCC thereby to reduce powerrequired to generate boosted potential VPP. Moreover, it is alsopossible to arrange the array 102 of word-line noise killer circuitsbetween the array 100 of memory cells and the array 101 of word-linedriving circuits, so as to suppress the noise interference between thearrays 100 and 101 without jeopardizing the high integration density.

In the first to fifth embodiments described above, the row decoders areNAND gates. Nonetheless, NOR gates can be employed instead. FIG. 22shows a word-line selecting circuit including a NOR gate 60 used as arow decoder. The NOR gate 60 comprises NMOSFETs. As shown in FIG. 22,the PMOSFET 61 included in a noise killer circuit is not directlyconnected to the output line a of the NOR gate 60. Rather, the PMOSFET61 is connected to the output line a by a VPP-based inverter 62.

In the above description, the words "connected" and "coupled" meaneither a direct connection or an indirect connection, unless followed bythe phrase "directly to" or "indirectly to."

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A semiconductor memory device comprising:aplurality of memory cells; a word line connected to the plurality ofmemory cells; a boosted voltage generating circuit which generates aconstant boosted potential higher than a power-supply potential; alevel-shifting circuit which level-shifts a precharge signal using thepower-supply potential to a boosted precharge signal using the constantboosted potential; a decoder circuit having address signal inputterminals to which address signals are inputted, a precharge signalinput terminal to which the boosted precharge signal is inputted, and anoutput terminal, the decoder circuit outputting one of the constantboosted potential and a ground potential from the output terminalthereof in accordance with the address signals and the boosted prechargesignal; a circuit having an inverter circuit, a P-channel transistor andan output terminal, the inverter circuit comprising an input terminalconnected to the output terminal of the decoder circuit and an outputterminal, the inverter circuit being supplied with the constant boostedpotential and the ground potential, the P-channel transistor comprisinga gate terminal connected to the output terminal of the inverter circuitand a current path, one end of the current path being supplied with theconstant boosted potential and another end of the current path beingconnected to the output terminal of the decoder circuit; and a word linedriving circuit which drives the word line in accordance with apotential at the output terminal of the circuit.
 2. The semiconductormemory device according to claim 1, wherein the output terminal of thecircuit is connected to the output terminal of the decoder circuit. 3.The semiconductor memory device according to claim 1, wherein the outputterminal of the circuit is connected to the output terminal of theinverter circuit.
 4. The semiconductor memory device according to claim1, wherein said decoder circuit comprises:a precharging circuit having acurrent path supplied with the constant boosted potential, andtransferring the constant boosted potential to the output terminal ofthe decoder circuit in accordance with the boosted precharge signal; anda decoding circuit having a current path supplied with the groundpotential to the output terminal of the decoder circuit in accordancewith the address signals.
 5. The semiconductor memory device accordingto claim 4, wherein the precharging circuit comprises a P-channeltransistor which transfers the constant boosted potential to the outputterminal of the decoder circuit in accordance with the boosted prechargesignal; andthe decoding circuit comprises series-connected N-channeltransistors which transfer the ground potential to the output terminalof the decoder circuit in accordance with the address signals.
 6. Asemiconductor memory device comprising:a plurality of memory cells; aword line connected to the plurality of memory cells; a boosted voltagegenerating circuit which generates a constant boosted potential higherthan a power-supply potential; a level-shifting circuit whichlevel-shifts a precharge signal using the power-supply potential to aboosted precharge signal using the constant boosted potential; a decodercircuit having address signal input terminals to which address signalsare inputted, a precharge signal input terminal to which the boostedprecharge signal is inputted, and an output terminal, the decodercircuit outputting one of the constant boosted potential and a groundpotential from the output terminal thereof in accordance with theaddress signals and the boosted precharge signal; a circuit having aninverter circuit, a P-channel transistor and an output terminal, theinverter circuit comprising an input terminal connected to the outputterminal of the decoder circuit and an output terminal, the invertercircuit being supplied with the constant boosted potential and theground potential, the P-channel transistor comprising a gate terminalconnected to the output terminal of the inverter circuit and a currentpath, one end of the current path being supplied with the constantboosted potential and another end of the current path being connected tothe output terminal of the decoder circuit; and a word line drivingcircuit associated with the output terminal of the circuit and drivingthe word line.
 7. The semiconductor memory device according to claim 6,wherein the output terminal of the circuit is connected to the outputterminal of the decoder circuit.
 8. The semiconductor memory deviceaccording to claim 6, wherein the output terminal of the circuit isconnected to the output terminal of the inverter circuit.
 9. Thesemiconductor memory device according to claim 6, wherein said decodercircuit comprises:a precharging circuit having a current path suppliedwith the constant boosted potential, and transferring the constantboosted potential to the output terminal of the decoder circuit inaccordance with the boosted precharge signal; and a decoding circuithaving a current path supplied with the ground potential to the outputterminal of the decoder circuit in accordance with the address signals.10. The semiconductor memory device according to claim 9, wherein theprecharging circuit comprises a P-channel transistor which transfers theconstant boosted potential to the output terminal of the decoder circuitin accordance with the boosted precharge signal; andthe decoding circuitcomprises series-connected N-channel transistors which transfer theground potential to the output terminal of the decoder circuit inaccordance with the address signals.
 11. A semiconductor memory devicecomprising:a first word line connected to a plurality of memory cells; asecond word line connected to a plurality of memory cells; a boostedvoltage generating circuit which generates a constant boosted potentialhigher than a power-supply potential; a level-shifting circuit whichlevel-shifts a precharge signal using the power-supply potential to aboosted precharge signal using the constant boosted potential; a firstdecoder circuit having address signal input terminals to which firstaddress signals are inputted, a precharge signal input terminal to whichthe boosted precharge signal is inputted, and an output terminal, thefirst decoder circuit outputting one of the constant boosted potentialand a ground potential from the output terminal thereof in accordancewith the first address signals and the boosted precharge signal; asecond decoder circuit having address signal input terminals to whichsecond address signals are inputted, a precharge signal input terminalto which the boosted precharge signal is inputted, and an outputterminal, the second decoder circuit outputting one of the constantboosted potential and the ground potential from the output terminalthereof in accordance with the second address signals and the boostedprecharge signal; a first circuit having a first inverter circuit, afirst P-channel transistor and an output terminal, the first invertercircuit comprising an input terminal connected to the output terminal ofthe first decoder circuit and an output terminal, the first invertercircuit being supplied with the constant boosted potential and theground potential, the first P-channel transistor comprising a gateterminal connected to the output terminal of the first inverter circuitand a current path, one end of the current path being supplied with theconstant boosted potential and another end of the current path beingconnected to the output terminal of the first decoder circuit; a secondcircuit having a second inverter circuit, a second P-channel transistorand an output terminal, the second inverter circuit comprising an inputterminal connected to the output terminal of the second decoder circuitand an output terminal, the second inverter circuit being supplied withthe constant boosted potential and the ground potential, the secondP-channel transistor comprising a gate terminal connected to the outputterminal of the second inverter circuit and a current path, one end ofthe current path being supplied with the constant boosted potential andanother end of the current path being connected to the output terminalof the second decoder circuit; a first word line driving circuit whichdrives the first word line in accordance with a potential at the outputterminal of the first circuit; and a second word line driving circuitwhich drives the second word line in accordance with a potential at theoutput terminal of the second circuit.
 12. The semiconductor memorydevice according to claim 11, wherein the output terminal of the firstcircuit is connected to the output terminal of the first decodercircuit, and the output terminal of the second circuit is connected tothe output terminal of the second decoder circuit.
 13. The semiconductormemory device according to claim 11, wherein the output terminal of thefirst circuit is connected to the output terminal of the first invertercircuit, and the output terminal of the second circuit is connected tothe output terminal of the second inverter circuit.
 14. Thesemiconductor memory device according to claim 11, wherein said firstdecoder circuit comprises:a first precharging circuit having a currentpath supplied with the constant boosted potential, and transferring theconstant boosted potential to the output terminal of the first decodercircuit in accordance with the boosted precharge signal; a firstdecoding circuit having a current path supplied with the groundpotential to the output terminal of the first decoder circuit inaccordance with the first address signals; a second precharging circuithaving a current path supplied with the constant boosted potential andtransferring the constant boosted potential to the output terminal ofthe second decoder circuit in accordance with the boosted prechargesignal; and a second decoding circuit having a current path suppliedwith the ground potential to the output terminal of the second decodercircuit in accordance with the second address signals.
 15. Thesemiconductor memory device according to claim 14, wherein the firstprecharging circuit comprises a P-channel transistor which transfers theconstant boosted potential to the output terminal of the first decodercircuit in accordance with the boosted precharge signal;the firstdecoding circuit comprises series-connected N-channel transistors whichtransfer the ground potential to the output terminal of the firstdecoder circuit in accordance with the first address signals; the secondprecharging circuit comprises a P-channel transistor which transfers theconstant boosted potential to the output terminal of the second decodercircuit in accordance with the boosted precharge signal; and the seconddecoding circuit comprises series-connected N-channel transistors whichtransfer the ground potential to the output terminal of the seconddecoder circuit in accordance with the second address signals.
 16. Asemiconductor memory device comprising:a first word line connected to aplurality of memory cells; a second word line connected to a pluralityof memory cells; a boosted voltage generating circuit which generates aconstant boosted potential higher than a power-supply potential; alevel-shifting circuit which level-shifts a precharge signal using thepower-supply potential to a boosted precharge signal using the constantboosted potential; a first decoder circuit having address signal inputterminals to which first address signals are inputted, a prechargesignal input terminal to which the boosted precharge signal is inputted,and an output terminal, the first decoder circuit outputting one of theconstant boosted potential and a ground potential from the outputterminal thereof in accordance with the first address signals and theboosted precharge signal; a second decoder circuit having address signalinput terminals to which second address signals are inputted, aprecharge signal input terminal to which the boosted precharge signal isinputted, and an output terminal, the second decoder circuit outputtingone of the constant boosted potential and the ground potential from theoutput terminal thereof in accordance with the second address signalsand the boosted precharge signal; a first circuit having a firstinverter circuit, a first P-channel transistor and an output terminal,the first inverter circuit comprising an input terminal connected to theoutput terminal of the first decoder circuit and an output terminal, thefirst inverter circuit being supplied with the constant boostedpotential and the ground potential, the first P-channel transistorcomprising a gate terminal connected to the output terminal of the firstinverter circuit and a current path, one end of the current path beingsupplied with the constant boosted potential and another end of thecurrent path being connected to the output terminal of the first decodercircuit; a second circuit having a second inverter circuit, a secondP-channel transistor and an output terminal, the second inverter circuitcomprising an input terminal connected to the output terminal of thesecond decoder circuit and an output terminal, the second invertercircuit being supplied with the constant boosted potential and theground potential, the second P-channel transistor comprising a gateterminal connected to the output terminal of the second inverter circuitand a current path, one end of the current path being supplied with theconstant boosted potential and another end of the current path beingconnected to the output terminal of the second decoder circuit; a firstword line driving circuit associated with the output terminal of thefirst circuit and driving the first word line; and a second word linedriving circuit associated with the output terminal of the secondcircuit and driving the second word line.
 17. The semiconductor memorydevice according to claim 16, wherein the output terminal of the firstcircuit is connected to the output terminal of the first decodercircuit, and the output terminal of the second circuit is connected tothe output terminal of the second decoder circuit.
 18. The semiconductormemory device according to claim 16, wherein the output terminal of thefirst circuit is connected to the output terminal of the first invertercircuit, and the output terminal of the second circuit is connected tothe output terminal of the second inverter circuit.
 19. Thesemiconductor memory device according to claim 16, wherein said firstdecoder circuit comprises:a first precharging circuit having a currentpath supplied with the constant boosted potential, and transferring theconstant boosted potential to the output terminal of the first decodercircuit in accordance with the boosted precharge signal; a firstdecoding circuit having a current path supplied with the groundpotential to the output terminal of the first decoder circuit inaccordance with the first address signals; a second precharging circuithaving a current path supplied with the constant boosted potential, andtransferring the constant boosted potential to the output terminal ofthe second decoder circuit in accordance with the boosted prechargesignal; and a second decoding circuit having a current path suppliedwith the ground potential to the output terminal of the second decodercircuit in accordance with the second address signals.
 20. Thesemiconductor memory device according to claim 19, wherein the firstprecharging circuit comprises a P-channel transistor which transfers theconstant boosted potential to the output terminal of the first decodercircuit in accordance with the boosted precharge signal;the firstdecoding circuit comprises series-connected N-channel transistors whichtransfer the ground potential to the output terminal of the firstdecoder circuit in accordance with the first address signals; the secondprecharging circuit comprises a P-channel transistor which transfers theconstant boosted potential to the output terminal of the second decodercircuit in accordance with the boosted precharge signal; and the seconddecoding circuit comprises series-connected N-channel transistors whichtransfer the ground potential to the output terminal of the seconddecoder circuit in accordance with the second address signals.